The present invention relates generally to implantable medical devices and methods of cardiac stimulus. More particularly, the present invention pertains to implantable medical pacing devices and methods that employ ventricular safety pacing (VSP) in cardiac stimulation.
Generally, in the heart, the sinus (or sinoartrial (SA)) node typically located near the junction of the superior vena cava and the right atrium) constitutes the primary natural pacemaker by which rhythmic electrical excitation is developed. The cardiac impulse arising from the sinus node is transmitted to the two atrial chambers (or atria) at the right and left sides of the heart. In response to excitation from the SA node, the atria contract, pumping blood from those chambers into the ventricles through the atrioventricular (AV) node, and via a conduction system comprising the bundle of His, or common bundle, the right and left bundle branches, and the Purkinje fibers. The transmitted impulse causes the ventricles to contract with the right ventricle pumping unoxygenated blood through the pulmonary artery to the lungs. The blood oxygenated by the lungs is carried via the pulmonary veins to the left atrium. The left ventricle then pumps oxygenated (arterial) blood through the aorta and the lesser arteries throughout the body.
The above action is repeated in a rhythmic cardiac cycle in which the atrial and ventricular chambers alternately contract and pump, and then relax and fill. One-way valves, between the atrial and ventricular chambers on the right and left sides of the heart, and at the exits of the right and left ventricles, prevent backflow of the blood as it moves through the heart and the circulatory system. This sinus node is spontaneously rhythmic, and the cardiac rhythm it generates is termed sinus rhythm. This capacity to produce spontaneous cardiac impulses is called rhythmicity. Some other cardiac tissue possess rhythmicity and hence constitute secondary natural pacemakers, but the sinus node is the primary natural pacemaker because it spontaneously generates electrical pulses at a faster rate. The secondary pacemakers tend to be inhibited by the more rapid rate at which impulses are generated by the sinus node.
Disruption of the natural pacemaking and propagation system as a result of aging or disease is commonly treated by artificial cardiac pacing, by which rhythmic electrical discharges are applied to the heart at a desired rate from an artificial pacemaker. A pacemaker is a medical device which delivers electrical pulses to an electrode that is implanted adjacent to or in the patient""s heart to stimulate the heart so that it will contract and beat at a desired rate. If the body""s natural pacemaker performs correctly, blood is oxygenated in the lungs and efficiently pumped by the heart to the body""s oxygen-demanding tissues. However, when the body""s natural pacemaker malfunctions, an implantable pacemaker often is required to properly stimulate the heart.
Implantable pacemakers are typically designed to operate using various different response methodologies, such as, for example, nonsynchronous or asynchronous (fixed rate), inhibited (stimulus generated in the absence of a specified cardiac activity), or triggered (stimulus delivered in response to a specific hemodynamic parameter). Generally, inhibited and triggered pacemakers may be grouped as xe2x80x9cdemandxe2x80x9d-type pacemakers, in which a pacing pulse is only generated when demanded by the heart. To determine when pacing is required by the pacemaker, demand pacemakers may sense various conditions such as heart rate, physical exertion, temperature, and the like. Moreover, pacemaker implementations range from the simple fixed rate, single chamber device that provides pacing with no sensing function, to highly complex models that provide fully-automatic dual chamber pacing and sensing functions. For example, such multiple chamber pacemakers are described in U.S. Pat. No. 4,928,688 to Mower entitled xe2x80x9cMethod and Apparatus for Treating Hemodynamic Dysfunction,xe2x80x9d issued May 29, 1990; U.S. Pat. No. 5,792,203 to Schroeppel entitled xe2x80x9cUniversal Programmable Cardiac Stimulation Device,xe2x80x9d issued Aug. 11, 1998; U.S. Pat. No. 5,893,882 to Peterson et al. entitled xe2x80x9cMethod and Apparatus for Diagnosis and Treatment of Arrhythmias,xe2x80x9d issued Apr. 13, 1999; and U.S. Pat. No. 6,081,748 to Struble et al. entitled xe2x80x9cMultiple Channel, Sequential Cardiac Pacing Systems,xe2x80x9d issued Jun. 27, 2000.
For example, a DDD pacer paces either chamber (atrium or ventricle) and senses in either chamber. Thus, a pacer in DDD mode, may pace the ventricle in response to electrical activity sensed in the atrium. Further, for example, a pacer operating in VVI mode, paces and senses in the ventricle, but its pacing is inhibited by spontaneous and electrical activity of the ventricle (i.e., intrinsic ventricular activity or events, wherein the ventricle paces itself naturally).
As such, it may be desired to sense in one cardiac chamber (e.g., detect electrical activity represented of contraction of a chamber and referred to as a xe2x80x9csensed eventxe2x80x9d) and, in response, pace (referred to as a xe2x80x9cpaced eventxe2x80x9d) in the same or different chamber. It also may be desired to pace at two electrode locations following a sensed event at one of the pacing electrodes or at a different electrode. For example, patients are often treated with pacemakers that include an electrode in each of the two atrial chambers and a third electrode in the right ventricle. Both atrial chambers usually are paced following a sensed event in either chamber.
Further, bi-ventricular pacing devices are also used for treatment of patients. For example, in such a bi-ventricular pacing apparatus, multiple implantable leads having electrodes associated with a part thereof are implanted to the respective chambers of a patient""s heart and coupled to respective circuitry for forming multiple channels for pacing and sensing, e.g., left ventricular channel, right atrial channel, etc. Such an exemplary implantable, four-channel cardiac pacemaker is described in U.S. Pat. No. 6,070,101 to Struble et al. entitled xe2x80x9cMultiple Channel, Sequential Cardiac Pacing Systems,xe2x80x9d issued May 30, 2000. For example, the distal end of a right atrial lead is attached to the right atrial wall and a right ventricular lead is passed through a vein into the right atrial chamber of the heart and into the right ventricle where its distal electrodes are fixed. Another lead is passed through a vein into the right atrial chamber of the heart, into the coronary sinus (CS), and then inferiorly into the great vein to extend a distal pair of left ventricular pace/sense electrodes alongside the left ventricular chamber and leave a proximal pair of left atrial pace/sense electrodes adjacent the left atrium. With such electrode placement, pacing and sensing can be performed in each chamber of the heart, enabling bi-ventricular pacing. For example, such bi-ventricular pacing may be performed following atrial sensed events or atrial paced events.
Typically in such types of pacing apparatus, if an intrinsic or pacing pulse occurs in one of the chambers, for example, the atrium, then this activity may be erroneously sensed in the other chambers due to cross-talk. In order to eliminate this type of error, in the past, pacemakers have been provided with blanking periods for blanking the sensor in one channel after a pacing pulse occurs in the other. This blanking period is usually referred to as the cross-channel blanking period. Following the blanking period, an alert period is normally designated during which the cardiac chamber of interest is monitored for intrinsic activity. If no such activity is sensed by the end of this alert, then a pacing pulse is applied to the chamber. However, one problem with such pacemakers and the use of blanking channels has been selecting the duration of the blanking period for a particular channel properly. If the blanking period is too short, a cross-channel artifact could be interpreted as an intrinsic activity and therefore pacing may be erroneously inhibited. On the other hand, if the blanking period is too long, intrinsic activity may be missed and the chamber may be paced when no such pacing is required. Either situation is undesirable physiologically.
Yet further, particularly in bi-ventricular pacing systems, e.g., systems which provide delivery of ventricular stimulus to both ventricular chambers following paced or sensed atrial events, a left ventricle lead is typically placed as described above, in a cardiac vein via the coronary sinus. Since the lead tip is in close proximity to the coronary sinus tractus, far-field coronary sinus/left atrial signals of significant amplitudes can potentially be sensed as ventricular activity and present inappropriate inhibition of bi-ventricular pacing. For example, in particular, when bipolar left ventricle leads are employed, the anode ring of the bipolar lead can be close to/or just within the coronary sinus system depending on tip-ring distance for the electrodes on the left ventricle lead. With the leads positioned in such a manner, atrial activity may be sensed using the left ventricle electrodes, taken as an intrinsic left ventricle event, and prevent or inhibit delivery of ventricular stimulus.
Further, for example, lead dislodgment may also lead to such mistaken sensing of ventricular events. For example, a left ventricular lead may be placed via the coronary sinus with a passive lead tip fixed in a cardiac vein. Leads are typically placed 1 to 4 centimeters within the vessels (or, generally, as far as possible). Either partial lead dislodgment (e.g., gradual pullback) or permanent lead dislodgment may result in an electrode location that is undesirable and conducive to over-sensing of left atrial activity. Therefore, once again, such over-sensing of atrial activity may lead to falsely sensed ventricular activity and the inhibition of the delivery of ventricular stimulus. As such, bi-ventricular stimulation may be intermittently or may be completely lost.
In many pacing apparatus, such as, for example, dual chamber pacing devices operating in DDD mode, ventricular safety pacing (VSP) is generally available and intended to prevent inappropriate inhibition of ventricular pacing by ensuring that an atrial paced event is followed by a ventricular paced event. When this VSP feature is on, ventricular sensing within a VSP window of typically 110 milliseconds following an atrial paced event causes ventricular pacing at the end of the VSP window (e.g., the 110 millisecond period).
For example, if the pacing apparatus is programmed with a paced AV interval (PAV=100 milliseconds) (i.e., the AV interval following an atrial paced event and defined as the time between the paced event and delivery of ventricular stimulus) that is less than the VSP window (e.g., 110 milliseconds), then the delivery of ventricular stimulus would occur at the end of the programmed PAV interval when ventricular sensing occurs during the VSP window.
In another example, if the pacing apparatus is programmed with a PAV interval (PAV=150 milliseconds) that is greater than the VSP window (VSP=110 milliseconds), then when ventricular sensing occurs during the VSP window, the delivery of ventricular stimulus would occur at the end of the VSP interval, and not at the time out of the PAV interval.
Further, with such conventional VSP, if no ventricular events are sensed during the VSP window and the PAV is greater in length than the VSP window, if a ventricular event is sensed during the PAV but after the VSP window, delivery of ventricular stimulus would be inhibited due to the sensed intrinsic ventricular event. This VSP feature is designed to ensure ventricular output in the event of noise sensing on the ventricular lead (e.g., cross-talk) within the VSP window or 110 milliseconds after an atrial paced event and outside the programmed ventricular blanking period.
Another example of a pacemaker having safety pacing is described in U.S. Pat. No. 5,782,881 to Lu et al., issued Jul. 21, 1998 and entitled xe2x80x9cPacemaker With Safety Pacing.xe2x80x9d As described therein, a monitoring window is defined during an AV delay during which signals sensed in a ventricular channel are monitored. If an abnormal signal is sensed during this window, certain features of the signal are analyzed to determine if its origin is intrinsic or due to cross-channel activity or noise. Cross-channel activity is ignored. If intrinsic cardiac activity is identified, then no pacing pulse or ventricular stimulation is applied. If no decision can be made as to the source of the cardiac activity, then delivery of stimulus is performed and ventricular pacing is not inhibited by the sensed activity.
The above-described VSP features may be inadequate in many circumstances. For example, conventional VSP features typically only occur when programmed on, and only following a paced atrial event. In other words, a VSP window is only utilized following delivery of pacing stimulus in the atrium and thus during a PAV interval. Such VSP features do not occur following atrial sensing or an atrial sensed event, where a timed sensed AV interval (SAV) is initiated.
Further, for example, in standard DDD pacemakers, when VSP is used, delivery of ventricular stimulus normally occurs following the expiration of the VSP window of 110 milliseconds, or at the termination of a PAV interval, whichever is less as previously described above. If the optimum PAV is programmed greater than 110 milliseconds (i.e., the PAV interval is longer than the VSP window), then normal delivery of stimulus at the termination of the 110 millisecond VSP window occurs too soon and not at termination of an optimum programmed PAV. In other words, such stimulus delivery at the termination of the VSP window will foreclose control of the heart by any intrinsic activity that may occur between the end of the VSP window and the termination of the PAV interval. As such, the optimized and programmed AV timing may be lost and competition to ventricular filling may occur.
Generally, optimized and programmed PAV intervals are significantly longer (e.g., 30-50 milliseconds) than SAV intervals. Fifty (50) milliseconds is generally required for slower conduction patients, for example, heart failure (HF) patients with conduction delays. For example, anticipated ranges for optimized SAV/PAV intervals in many patients may be, for example, SAV 80-130 milliseconds/PAV 130-180 milliseconds. Therefore, the problems associated with an optimum PAV programmed at a length greater than 110 milliseconds are readily apparent.
Yet further, as VSP does not typically occur following atrial sensing as described above, then any inappropriate over-sensing of intrinsic coronary sinus/left atrial signals during an SAV interval will result in the mistaken belief that a ventricular event has occurred and ventricular stimulation therapy is inhibited. This is particularly undesirable in atrial bi-ventricular pacing which is typically intended for heart failure patients with left bundle branch block (LBBB) and/or intraventricular conduction delay (IVCD) and intact sinus rhythm (SR). The expected majority of the therapy to be delivered in such patients is generally associated with sensed atrial events and operating with an SAV interval as opposed to paced atrial events operating with a PAV interval. As therapy operation with a PAV following a paced atrial event occurs only in the minority of such patients, use of standard or conventional VSP features for atrial bi-ventricular pacing that result only after atrial paced events operating with a PAV interval is limited.
Table I below lists U.S. patents relating to multiple chamber pacing devices and devices and methods having VSP features.
All references listed in Table I, and elsewhere herein, are incorporated by reference in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Embodiments, and claims set forth below, at least some of the devices and methods disclosed in the references of Table I and elsewhere herein may be modified advantageously by using the teachings of the present invention. However, the listing of any such references in Table I, or elsewhere herein, is by no means an indication that such references are prior art to the present invention.
The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the prior art with respect to implantable medical device pacing techniques and, in particular, current ventricular safety pacing (VSP) techniques. One of such problems is that the current pacing apparatus generally apply VSP following only paced atrial events. Further, for example, pacing at the termination of the VSP window using current techniques may also not be adequate, e.g., when the PAV interval is longer than the VSP window. Yet further, for example, other problems involve the general inhibition of bi-ventricular stimulation therapy due to inappropriate over-sensing of intrinsic coronary sinus/lower left atrial signals during AV intervals and inhibition of ventricular stimulus due at least in part to lead dislodgment and inappropriate sensing thereafter.
In comparison to known VSP techniques, various embodiments of the present invention may provide one or more of the following advantages. For example, VSP according to the present invention always ensures pacing therapy at the optimized programmed SAV and PAV intervals, i.e., SAV and PAV delays. Further, such committed delivery of ventricular stimulation therapy at the optimized SAV and PAV intervals is ensured even with the occurrence of inappropriate coronary sinus/left atrial far-field sensing, even with the occurrence of post-atrial paced ringing, even with the occurrence and sensing of coronary sinus/left atrial intrinsic signals; etc. This ensured ventricular pacing therapy at the optimized programmed SAV and PAV intervals is provided by not only establishing committed VSP following a paced atrial event, but also following a sensed atrial event.
Some embodiments of the method of the present invention include one or more of the following features: providing a sensed AV delay following an atrial sensed event with the sensed AV delay being a predetermined time period initiated thereby; defining a VSP window during at least an initial portion of a sensed AV delay with the sensed AV delay further including a remainder portion thereof subsequent to the initial portion; sensing ventricular events during the sensed AV delay; delivering ventricular stimulus upon expiration of the sensed AV delay if no ventricular events are sensed during the VSP window defined during the initial portion of the sensed AV delay and the reminder portion thereof; inhibiting the delivery of ventricular stimulus upon expiration of a sensed AV delay if no ventricular events are sensed during the VSP window but a ventricular event is sensed during a remainder portion of the sensed AV delay; committing to the delivery of a ventricular stimulus upon expiration of a sensed AV delay if a ventricular event is sensed during a VSP window; defining a VSP window during an initial portion of a sensed AV delay that is 110 milliseconds; and defining a sensed AV delay that is equal to or greater than a VSP window.
Other embodiments of the method of the present invention include one or more of the following features: providing a paced AV delay following an atrial paced event with the paced AV delay being a predetermined time period initiated thereby; defining a VSP window during at least an initial portion of the paced AV delay with the paced AV delay further comprising a remainder portion thereof subsequent to the initial portion; sensing ventricular events during the paced AV delay; delivering ventricular stimulus upon expiration of the paced AV delay if no ventricular events are sensed during a VSP window defined during an initial portion of a paced AV delay and the remainder portion thereof; inhibiting the delivery of ventricular stimulus upon expiration of the paced AV delay if a ventricular event is not sensed during the VSP window but a ventricular event is sensed during the remainder portion of the paced AV delay; committing to delivery of ventricular stimulus upon expiration of the paced AV delay if a ventricular event is sensed during the VSP window; defining a paced AV delay and a sensed AV delay that are both greater than a VSP window; defining a paced AV delay that is greater than the sensed AV delay; delivering bi-ventricular stimulus; and providing an AV delay initiated by occurrence of either an atrial sensed event or an atrial paced event with the AV delay being a programmed time period whose length is varied depending upon whether the AV delay is initiated by the occurrence of an atrial sensed event or is initiated by the occurrence of an atrial paced event.
Further, some embodiments of an apparatus according to the present invention include one or more of the following features: a dual chamber pacing apparatus; atrial pacing and sensing circuitry to generate atrial pacing pulses and sense atrial events; ventricular pacing and sensing circuitry to generate ventricular pacing pulses and sense ventricular events; control circuitry operable to provide a sensed AV delay following an atrial sensed event detected using the atrial sense circuitry with the sensed AV delay being a predetermined time period initiated by the atrial sensed event; control circuitry operable to define a VSP window during at least an initial portion of the sensed AV delay with the sensed AV delay further including a remainder portion thereof subsequent to the initial portion; control circuitry operable to detect ventricular events using the ventricular sensing circuitry during a sensed AV delay; control circuitry operable to control delivery of ventricular stimulus using the ventricular pacing circuitry upon expiration of a sensed AV delay such that if no ventricular events are detected during the VSP window defined during the initial portion of the sensed AV delay and the remainder portion thereof then ventricular stimulus is deliver at the expiration of the sensed AV delay; control circuitry operable to control delivery of ventricular stimulus using the ventricular pacing circuitry upon expiration of a sensed AV delay such that if a ventricular event is not detected during the VSP window but a ventricular event is detected during the remainder portion of the sensed AV delay then delivery of ventricular stimulus upon expiration of the sensed AV delay is inhibited; and control circuitry operable to control delivery of ventricular stimulus using the ventricular pacing circuitry upon expiration of a sensed AV delay such that if a ventricular event is sensed by the ventricular sensing circuitry during the VSP window then the ventricular pacing circuitry is committed to delivery of ventricular stimulus upon expiration of the sensed AV delay.
Yet further, other embodiments of the apparatus may include one or more of the following features: control circuitry operable to provide a paced AV delay following an atrial paced event with the paced AV delay being a predetermined time period initiated by the occurrence of an atrial paced event resulting from the generation of atrial pacing pulses by the atrial pacing circuitry; control circuitry operable to define a VSP window during at least an initial portion of a paced AV delay with the paced AV delay further including a remainder portion thereof subsequent to an initial portion; control circuitry operable to control delivery of ventricular stimulus using the ventricular pacing circuitry upon expiration of a paced AV delay such that if no ventricular events are detected during the VSP window defined during the initial portion of the paced AV delay and the remainder portion thereof then ventricular stimulus is deliver at the expiration of the paced AV delay; control circuitry operable to control delivery of ventricular stimulus using the ventricular pacing circuitry upon expiration of a paced AV delay such that if a ventricular event is not detected during the VSP window but a ventricular event is detected during the remainder portion of the paced AV delay then delivery of ventricular stimulus upon expiration of the paced AV delay is inhibited; control circuitry operable to control delivery of ventricular stimulus using the ventricular pacing circuitry upon expiration of a paced AV delay such that if a ventricular event is sensed by the ventricular sensing circuitry during the VSP window then the ventricular pacing circuitry is committed to delivery of ventricular stimulus upon expiration of the paced AV delay; bi-ventricular pacing and sensing circuitry to generate bi-ventricular pacing pulses and sense ventricular events; and control circuitry operable to provide an AV delay initiated by occurrence of either an atrial sensed event detected by atrial sensing circuitry or an atrial paced event associated with the generation of atrial pacing pulses using atrial pacing circuitry with the AV delay being a programmed time period whose length is varied depending upon whether the AV delay is initiated by the occurrence of an atrial sensed event or is initiated by the occurrence of an atrial paced event.
The above summary of the present invention is not intended to describe each embodiment or every implementation of the present invention. Advantages, together with a more complete understanding of the invention, will become apparent and appreciated by referring to the following detailed description and claims taken in conjunction with the accompanying drawings.